Communications systems exist that can use directional antennas to track a transmit terminal transmitting a radio frequency (RF) signal as part of a data link between the transmit terminal and a receive terminal. A directional antenna can be adjusted about one or more axes. When a transmission terminal (e.g., a satellite or transmitting tower) is in a relatively fixed position and a directional antenna is also in a relatively fixed position, then open-loop pointing of the directional antenna may be used.
Open-loop antenna pointing techniques are extremely useful and cost effective if the subject antenna mounting position and mounting base are known precisely, thus not requiring an antenna tracking feedback system. These techniques are therefore useful if the cumulative pointing errors are much smaller than the antenna bandwidth, providing acceptable pointing losses.
There are times when an antenna is mounted on a mobile platform, such as when the transmission terminal is disposed in an aircraft or satellite. Open-loop antenna pointing techniques do not have feedback and therefore tend not to function well when one or more of the antenna or transmission terminal is moving. In this situation, closed-loop antenna pointing techniques are typically used to allow a directional antenna to track an opposing transmission or reception terminal.
With regard to closed-loop pointing techniques, most closed loop pointing systems rely on signal strength indication from automatic gain control (AGC) loops to provide closed-loop error feedback to an antenna servo control loop. The antenna servo control loop then controls the directional antenna to track the transmission terminal.
While closed-loop antenna pointing techniques are beneficial, these techniques can also be relatively expensive and may be limited in certain areas. Thus, it would be beneficial to provide improvements to antenna tracking using pointing techniques such as open-loop or closed-loop antenna pointing.